Highly Vented Truss Wall Honeycomb Structures and Methods of Fabrication

ABSTRACT

A vented honeycomb structure with a plurality of honeycomb cells arranged in a hierarchical order and having a plurality of truss walls, each truss wall including a plurality of members. The vented honeycomb structure is fabricated by joining a plurality of sheets of trusses using any one of an expansion, a corrugation, and a slotting process. Fabrication can also occur by deposition, casting, additive, extrusion, or aligning and joining methods. The honeycomb cells, truss walls, truss wall openings, and truss wall members can be functionally graded.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/503,982, filed on Jul. 1, 2011. Thespecification and drawings of the provisional patent application arespecifically incorporated by reference herein.

TECHNICAL FIELD

Embodiments of the invention generally relate to improvedstructural/multifunctional material designs and methods for fabricatingthem. More particularly, the embodiments relate to the use of trussesfor the walls of honeycombs and lightweight structures fabricated fromthem.

BACKGROUND OF THE INVENTION

A truss is a framework of members fastened together at their ends tosupport loads. A plane truss has all members lying in a single geometricplane whereas a space truss has members lying in three-dimensions. Trussmembers are typically long, straight, slender, and have constantcross-section. They can be fastened by welding, riveting, bolting (oftengusset plates are used), or other means. Members support load bytension/compression only for maximum structural efficiency (bending isnot as efficient). These robust types of structures provide greaterstiffness, strength, and damage tolerance over other structural choicesat lower weight and cost, are relatively straightforward to analyze,design, and fabricate, while their exposed interior provides much openspace for other functionalities. Skyscraper framing, bridges, roofsupports, transmission line towers, radio antennas, etc. are allcommonly made from trusses. Classic examples include the Eiffel Towerand cellular geodesic domes.

Honeycombs are cellular solids made from a collection of thin wall openprismatic cells nested together to fill a plane. Exceptionally stiff andstrong for their weight, they can also be multifunctional and do muchmore than just support loads. Aerospace (e.g., aircraft, rockets,spacecraft, etc.) and other industries widely benefit from this form ofconstruction where weight savings is crucial. Some of the many honeycombapplications include sandwich structure cores, impact energy absorbers,flow aligners, filters, insulating panels, radio frequency shields,sound barriers, catalyst support medium, heat exchangers, and acousticdampeners.

When facing skins are attached to conventional honeycomb cores, thefabrication environment (e.g., humid air, volatile organic compounds,etc.) is trapped within. In space applications, pressure differentialbetween the core and ambient during ascent can lead to missioncatastrophic failure. In the near vacuum of space, core release cancontaminate sensitive equipment. With time and exposure, the serviceenvironment (e.g., humid air) can also be trapped through ingress anddiffusion. Aircraft control surfaces, helicopter rotor blades, etc., areall susceptible to moisture accumulation which adds weight, degradesadhesives, accelerates corrosion, steams/freezes, etc.Pressurization/depressurization and heating/cooling cycles (e.g.,ground-air-ground) exacerbate the issue. A simple “tap” test sometimesexposes the “dead zones.” One way to repair a wet honeycomb coreinvolves introducing holes into the facing skins, puncturing the cellwalls, heating to remove the moisture, and then patching. However,damage caused by the moisture largely remains, steam pressure buildupduring heating or patching weakens the panels, the paths for moistureingress are not resolved, and the problem is likely to repeat. One canfabricate the honeycomb with porous, perforated, slotted, or drilledwalls (or facing skins), and/or offset honeycomb layers, but most ofthese “breathable” versions have limited fluid throughput and cost more.Furthermore, holes or other alterations tend to concentrate stress andstructural integrity may suffer.

SUMMARY

In exemplary embodiments disclosed herein, honeycomb structures includetruss walls. The trusses can include structures that are solid, hollow,porous, or combinations thereof. The trusses can be fabricated fromvarious materials and combinations thereof. The cross-sectional shapesof the trusses can include hexagonal, triangular, square, rectangular,circular, elliptical, and other shapes and combinations thereof. Trusswall openings can include hexagonal, triangular, square, rectangular,circular, elliptical, angular, and other shapes and combinationsthereof. Honeycomb cell shapes can include hexagonal, triangular,square, rectangular, circular, elliptical, angular, and other shapes andcombinations thereof. The honeycomb cells, truss wall openings, trusswall members, and/or truss walls can be functionally graded. Thehoneycomb structure can be flat, tapered, curved, or combinationsthereof, and have one or more perimeter-oriented facing skins.

In one embodiment, a vented honeycomb structure includes a plurality ofhoneycomb cells arranged in a hierarchical order and having a pluralityof truss walls, each truss wall including a plurality of members. Thehoneycomb cells, the truss wall openings, the truss wall members, andthe truss walls can be functionally graded in some embodiments.

In one embodiment, a method is provided for fabricating a vented trusswall honeycomb structure having a plurality of honeycomb cells arrangedin a hierarchical order and having a plurality of truss walls, eachtruss wall including a plurality of members and a plurality of trusswall openings. A plurality of sheets of trusses is provided and thehoneycomb structure is formed by joining the plurality of sheets usingany one of an expansion, a corrugation, and a slotting process.Fabrication can also occur by deposition, casting, additive, extrusion,or aligning and joining methods in some embodiments. The honeycombcells, the truss wall openings, the truss wall members, and the trusswalls can be functionally graded in some embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages and aspects of the embodiments of thedisclosure will become apparent and more readily appreciated from thefollowing detailed description of the embodiments taken in conjunctionwith the accompanying drawings, as follows.

FIG. 1A illustrates solid wall and exemplary truss wall honeycombstructures.

FIG. 1B illustrates a graded truss wall honeycomb structure in anexemplary embodiment.

FIG. 2 illustrates a sandwich structure with a bias) (±45° orientedtruss wall honeycomb core in an exemplary embodiment.

FIG. 3 illustrates a multifunctional sandwich structure providing loadsupport plus cooling in an exemplary embodiment.

FIG. 4 illustrates a process for fabricating honeycomb cores fromslotted truss sheets in accordance with an exemplary embodiment.

FIG. 5 illustrates test samples for solid wall and exemplary truss wallhoneycomb structures.

FIG. 6 illustrates the crushing behavior for solid wall and exemplarytruss wall honeycomb structures.

FIG. 7 illustrates stress-strain behavior for crushed solid wall andexemplary truss wall honeycomb structures.

FIG. 8 illustrates the normalized (stress/yield) stress-strain behaviorfor crushed solid wall and exemplary truss wall honeycomb structures.

DETAILED DESCRIPTION

The following description is provided as an enabling teaching ofembodiments of the invention including the best, currently knownembodiment. Those skilled in the relevant art will recognize that manychanges can be made to the embodiments described, while still obtainingthe beneficial results. It will also be apparent that some of thedesired benefits of the embodiments described can be obtained byselecting some of the features of the embodiments without utilizingother features. Accordingly, those who work in the art will recognizethat many modifications and adaptations to the embodiments described arepossible and may even be desirable in certain circumstances. Thus, thefollowing description is provided as illustrative of the principles ofthe invention and not in limitation thereof, since the scope of theinvention is defined by the claims.

Many honeycomb structures have their honeycomb core bonded to facings(skins). Unvented honeycomb sandwich structures use an unvented core sothat there is no air transfer from cell to cell and there is no ventingto the exterior of the panel. A perforated honeycomb core alone may notprovide a vented structure unless the panel provides exterior venting aswell. Partially vented honeycomb structures provide some venting but notenough to accommodate pressure differentials between internal andexterior surfaces.

Vented honeycomb structures can use perforated, slotted, or poroushoneycomb cores through which air can flow freely from cell to cell at arate corresponding to a pressure drop between internal and exteriorsurfaces. In exemplary embodiments, many porous sheet types, joiningmethods, and wall/cell geometries are possible for fabricating such astructure. Venting to the exterior is provided either through the skinor panel edge members.

Mechanical properties are influenced by the base material and itsdistribution, imperfections, and defects. The most weight efficientstructures favor structural hierarchy, i.e., elements/members whichthemselves have structure. Cancellous bone, fibrous composites, and theEiffel tower are all examples of hierarchical structures. Whendeformation is dominated by substructure bending, neither relativestiffness nor strength benefit from structural hierarchy. Closed andopen cell foams undergo mechanical properties knockdown (thesemechanical properties scale much less than linearly with density)because of this. With foaming, control over the distribution of cellsize and wall/ligament geometry is inherently difficult. However, whenelements/members are favorably oriented (e.g., space truss), and/or flatand straight (e.g., honeycomb), mechanical properties can scale linearlywith density. Furthermore, the first few levels of hierarchical order(i.e., number of levels of scale with recognized structure) can yielddramatic strength to weight improvements. Many short elements/membersresist buckling better than a few long members. Many short members alsoimprove safety though structural redundancy, although weight specificstiffness remains largely unchanged.

The ability to organize, characterize and manipulate mattersystematically at a small scale is a worthwhile endeavor but requireseffort and resources. Frequently, compromises are made by joiningrelatively small amounts of stochastic matter in an organized way. Forexample, honeycomb cell walls can be made from a stochastic arrangementof matter, e.g., metal grains or aramid paper fibers, although the cellgeometries themselves are highly organized. Other successful examplesinclude fibrous composites and structural sandwich panels. Withhierarchy, simple and affordable processes are sought. Functionalgrading characterized by gradual compositional or structural variationsover the volume leads to gradually changing properties of the material.

Hierarchical truss concepts can extend to highly vented honeycombstructures, such as those illustrated in FIG. 1, with addedfunctionality such as space for fuel storage, coolant flow, wiring andpiping, etc. In exemplary embodiments, efficient trusses are used forthe walls of efficient honeycombs. The trusses can be, but are notlimited to, solid, hollow, porous, or combinations thereof. The trussescan be fabricated from, but are not limited to, a natural material,metal, ceramic, polymer, elastomer, glass, paper, composite,semiconductor, or combinations thereof. The cross-sectional shapes ofthe trusses can be, but are not limited to, hexagonal, triangular,square, rectangular, circular, elliptical, angular, I-beam, Z-section,C-section, H-section, T-section, L-section, hat-section, other shapes,or combinations thereof. Truss wall openings can be, but are not limitedto, hexagonal, triangular, square, rectangular, circular, elliptical,other shapes, or combinations thereof. Honeycomb cell shapes can be, butare not limited to, hexagonal, triangular, square, rectangular,circular, elliptical, other shapes, or combinations thereof. FIG. 1Adepicts truss wall honeycomb cell shapes that are hexagonal, with trusswall openings that are hexagonal, triangular, and square (or diamond).In exemplary embodiments, honeycomb cells, truss wall openings, trusswall members, and/or truss walls can be functionally graded, i.e.,composition and structure varying gradually over volume resulting inchanges in the properties of the material. FIG. 1B illustrates a gradedhoneycomb structure. The honeycomb structure can be flat, tapered,curved, or combinations thereof, and have one or more perimeter-orientedfacing skins. FIG. 2 illustrates facing skins on a hexagonal cell corestructure. The sandwich structure depicted includes bias) (±45° orientedtruss walls. Truss wall honeycombs can be made by expansion,corrugation, or slotting processes; by sacrificial or retained templatedeposition processes, by casting, by additive methods, by extrusion, orby aligning and joining methods. FIG. 3 illustrates a multifunctionalsandwich structure providing load support plus cooling. FIG. 4illustrates a process for fabricating honeycomb cores from slotted trusssheets.

One approach for providing sheets of trusses is based upon a recognitionthat high structural quality porous objects have already been made formany years by taking filaments (e.g., wrought metal wires) and weaving,braiding, or knitting them. Woven fiberglass cloth, braided metalcables, and knitted polyester garments are good examples. The textileapproaches used to create such articles are very well established andaffordable. Furthermore, a host of base material choices are availablealong with a wide variety of filament arrangements and mixes.Conventional textiles become rigid sheets of trusses when their filamentcontacts are appropriately bonded (similar to fastening the members of atruss). Straight, slender filaments are desired.

In one embodiment, plain square mesh woven wire cloth of type 304stainless steel with 0.17 mm (0.0065 in) diameter wires and having 11.8mesh/cm (30 mesh/in) was bias cut, cleaned, and then lightly sprayedwith a mix of −140 mesh Nicrobraz® 51 brazing filler metal (composition:Ni-25Cr-10P 10P wt. %) and Nicrobraz® Cement 520, both available fromWall Colmonoy Corporation (Madison Heights, Mich.). Strips were heated(ramp at 15° C./min; hold at 550° C. for one hour with an argon (Ar)purge to volatilize the cement; hold at 1100° C. for one hour in vacuumto braze) in a Ti gettered vacuum furnace (6 in diameter quartz tube;diffusion pumping system with liquid nitrogen trap; vacuum capability<10⁻⁶ Torr). By bonding the wire contacts, rigid sheets of miniaturetrusses are made. After cooling, the strips were corrugated, sprayed,stacked, and brazed again.

As illustrated in FIG. 5, the test sample had 6.4 mm (0.25 in) cells,was 51.2 mm×45.2 mm×76.5 mm (thick) with 31.5 g mass (0.178 g/cm³ or11.1 pcf). With 7.9 g/cm³ for type 304 stainless steel, the relativedensity was approximately 2.3%. Commercial expansion process honeycombmade from 0.064 mm (0.0025 in) thick aluminum alloy foil with 6.4 mm(0.25 in) cells offered comparison. The test sample was 54.9 mm×43.0mm×76.3 mm (thick) with 12.9 g mass (0.0716 g/cm³ or 4.5 pcf). With 2.7g/cm³ for aluminum alloys, the relative density was approximately 2.7%.

An Instron Corporation (Norwood, Mass.) 8802 test system equipped with a±25 kN load cell, flat compression platens, and FastTrack™ 8800 digitalcontrol/acquisition was used for testing. Samples were pre-loaded to 45N (ASTM D 7336/D 7336M-07), then crushed at 5 min/min. Photographs andload-actuator displacement (converted to stress-strain), illustrated inFIGS. 6 and 7, respectively, were digitally recorded. The barecompressive strength for the solid wall honeycomb was 4.83 MPa at 0.57%,crush strength was approximately 1.7 MPa, and the absorbed energy at 75%stroke was 1.30 J/cm³ or 18.2 J/g. For the truss wall honeycomb,compressive strength was 1.20 MPa at 4.21%, crush strength wasapproximately 1.1 MPa, and absorbed energy was 0.84 J/cm³ or 4.7 J/g.

Plastic buckling collapse stress scales with parent alloy yieldstrength. Annealed type 304 stainless steel yields at 205 MPa which issomewhat less than extra hard honeycomb foils like aluminum alloy5052-H39 or aluminum alloy 5056-H39 (e.g., values for the reported H38temper are 255 MPa and 345 MPa, respectively). Tensile tests conductedon aluminum alloy foils extracted from the commercial honeycombconfirmed a yield strength near the upper end of this range. FIG. 7illustrates stress-strain behavior for crushed sold wall and truss wallhoneycomb structures. Dividing stress by parent alloy yield strengthreveals very similar normalized crushing performance. FIG. 8 illustratesthe normalized (stress/yield) stress-strain behavior for crushed solidwall and exemplary truss wall honeycomb structures. Additionally, thetruss wall honeycomb exhibited a smoother crushing response with littleinitial peak stress (commercial energy absorbing honeycombs are commonlypre-crushed prior to field). The truss wall honeycomb is highly ventedhaving much interconnected porosity, and its walls can be tailored. Forexample, bias oriented trusses resist shear for a good sandwich core.FIG. 2 illustrates a sandwich structure with a bias) (±45° orientedtruss wall honeycomb core.

Another embodiment for providing sheets of trusses involves making holesin thin solid sheets. This can be done in a variety of ways includingdrilling, punching, perforating, laser or water jet cutting, chemicaletching, etc. Other methods such as deposition, casting, rapidprototyping, powder sintering, extrusion, etc., can also work. Sheets ofmicro tubing can be used to create hollow trusses for improvedefficiency and application. Expansion methods (e.g., expanded metals)are particularly attractive because unlike punching, base material isnot lost to keep costs down. The process involves precision shearing ofa solid sheet in such a way that causes the material to slit andstretch, leaving diamond shaped voids surrounded by interconnectedstrands of material (i.e., plane truss members). Paper can also beexpanded but does not always remain stretched.

Brazing coil (#22-F 6951-F/4343) comprising precipitation hardenablealuminum alloy 6951 clad on both sides (approximately 10% thickness perside) with flux brazing aluminum alloy 4343 was obtained from LynchMetals Incorporated (Union, N.J.). The material was 0.152 mm (0.006 in)thick and has a recommended flux brazing range of 593-616° C. Portionsof the brazing coil were referred to Dexmet Corporation (Wallingford,Conn.) for precision micro expansion (a process that works for mostmetals and polymers). Dexmet fabricated MicroGrid® 6 Al 12-125 where 6is original coil thickness (0.006 in), Al is aluminum, 12 is strandwidth (0.012 in), and 125 (0.125 in) is LWD dimension. The microexpanded material had 0.0625 in for SWD dimension, was 0.0120 in thick,had strands with nearly rectangular cross-section (0.012 in by 0.006in), and 0.102 g/in² mass per area. This equates to 0.519 g/cm³ byvolume. Post flattening nearly doubled the density by compressing toalmost the original coil thickness. It should be noted that strandshaving a square cross-section whose length is just short enough to avoida buckling failure (yielding failure is preferred instead) are favoredfor making even lighter, more efficient truss structures.

To fabricate a truss wall honeycomb structure, a micro expanded brazingcoil is corrugated (this also flattens), cleaned, stacked/aligned, andthen salt bath dip brazed using molten Alu-Braze 860® (available fromHeatbath Corporation, Indian Orchard, Mass.). Dip brazing occurs atabout 600° C. for a short time, followed by draining, cooling, andcleaning. The resulting bonded truss wall honeycomb structure has largeamounts of open, interconnected wall porosity and density of about 0.06g/cm³. With 2.7 g/cm³ for aluminum alloys, relative density isapproximately 2%. Polymer base adhesives and appropriate surfacepretreatments like those used for bonding honeycomb foils also work,however, polymers become brittle when cold, soft when hot. Metallurgicalbonding increases the temperature range capability. Vacuum or controlledatmosphere brazing provides another metallurgical option. Soldering,welding, diffusion bonding, chemical welding, and pressing can alsowork.

In other embodiments, a honeycomb truss can be fabricated by depositiononto a sacrificial or retained truss wall honeycomb template (e.g.,electroless nickel plating), by casting material into molds with trusswall honeycomb shaped cavities, by additive fabrication such as powdersintering or rapid prototyping, by extrusion, or by aligning and joiningmethods. Deposition onto sacrificial templates is one way to producetruss members that are hollow.

The corresponding structures, materials, acts, and equivalents of allmeans plus function elements in any claims below are intended to includeany structure, material, or acts for performing the function incombination with other claim elements as specifically claimed. Thoseskilled in the art will appreciate that many modifications to theexemplary embodiments are possible without departing from the scope ofthe present invention.

In addition, it is possible to use some of the features of theembodiments disclosed without the corresponding use of the otherfeatures. Accordingly, the foregoing description of the exemplaryembodiments is provided for the purpose of illustrating the principlesof the invention, and not in limitation thereof, since the scope of theinvention is defined solely by the appended claims.

1. A vented honeycomb structure comprising a plurality of honeycombcells arranged in a hierarchical order and having a plurality of trusswalls, each truss wall including a plurality of members.
 2. The ventedhoneycomb structure of claim 1 wherein the truss wall members are atleast one of solid, hollow, and porous.
 3. The vented honeycombstructure of claim 1 wherein the truss wall members comprise at leastone of a natural material, a metal, a ceramic, a polymer, an elastomer,a glass, a paper, a composite, and a semiconductor.
 4. The ventedhoneycomb structure of claim 1 wherein the truss wall members comprise across-section comprising at least one of a hexagonal, a triangular, asquare, a rectangular, a circular, an elliptical, an angular, an I-beam,a Z-section, a C-section, a H-section, a T-section, an L-section, and ahat-section shape.
 5. The vented honeycomb structure of claim 1 furthercomprising truss wall openings that include at least one of a hexagonal,a triangular, a square, a rectangular, a circular, and an ellipticalshape.
 6. The vented honeycomb structure of claim 1 wherein thehoneycomb cells comprise at least one of a hexagonal, a triangular, asquare, a rectangular, a circular, and an elliptical shape.
 7. Thevented honeycomb structure of claim 5 wherein at least one of thehoneycomb cells, the truss wall openings, the truss wall members, andthe truss walls is functionally graded.
 8. The vented honeycombstructure of claim 1 wherein said honeycomb structure is at least one offlat, tapered, and curved.
 9. The vented honeycomb structure of claim 1further comprising at least one perimeter-oriented facing skin.
 10. Thevented honeycomb structure of claim 9 wherein the honeycomb cells andfacing skins form a sandwich structure comprising a plurality of trusswalls.
 11. The vented honeycomb structure of claim 10 wherein theplurality of truss walls are bias-oriented at ±45°.
 12. A method offabricating a vented truss wall honeycomb structure having a pluralityof honeycomb cells arranged in a hierarchical order and having aplurality of truss walls, each truss wall including a plurality ofmembers and a plurality of truss wall openings, the method comprising:providing a plurality of sheets of trusses; and joining the plurality ofsheets using any one of an expansion, a corrugation, and a slottingprocess to form the honeycomb structure.
 13. The method of fabricating avented truss wall honeycomb structure of claim 12 wherein the pluralityof sheets are provided by joining a plurality of trusses by at least oneof soldering, brazing, welding, diffusion bonding, chemical welding,adhesives, and pressing.
 14. The method of fabricating a vented trusswall honeycomb structure of claim 12 wherein joining the plurality ofsheets comprises at least one of soldering, brazing, welding, diffusionbonding, chemical welding, adhesives, and pressing.
 15. The method offabricating a vented truss wall honeycomb structure of claim 12 furthercomprising joining one or more perimeter-oriented facing skins to thehoneycomb structure.
 16. The method of fabricating a vented truss wallhoneycomb structure of claim 15 wherein joining the facing skins to thehoneycomb structure comprises at least one of soldering, brazing,welding, diffusion bonding, chemical welding, adhesives, and pressing.17. The method of fabricating a vented truss wall honeycomb structure ofclaim 12 further comprising functionally grading at least one of thehoneycomb cells, the truss wall openings, the truss wall members, andthe truss walls.
 18. A method of fabricating a vented truss wallhoneycomb structure having a plurality of honeycomb cells arranged in ahierarchical order and having a plurality of truss walls, each trusswall including a plurality of members and a plurality of truss wallopenings, the method comprising: providing a sacrificial or retainedtruss wall honeycomb structure; depositing one or more materials ontothe sacrificial or retained truss wall honeycomb structure to form thetruss wall members; and removing the sacrificial structure or preservingthe retained truss wall structure.
 19. The method of fabricating avented truss wall honeycomb structure of claim 18 further comprisingjoining one or more perimeter-oriented facing skins to the honeycombstructure.
 20. The method of fabricating a vented truss wall honeycombstructure of claim 19 wherein joining the facing skins to the honeycombstructure comprises at least one of soldering, brazing, welding,diffusion bonding, chemical welding, adhesives, and pressing.
 21. Themethod of fabricating a vented truss wall honeycomb structure of claim18 further comprising functionally grading at least one of the honeycombcells, the truss wall openings, the truss wall members, and the trusswalls.
 22. A method of fabricating a truss wall honeycomb structurehaving a plurality of honeycomb cells arranged in a hierarchical orderand having a plurality of truss walls, each truss wall including aplurality of members and a plurality of truss wall openings, the methodcomprising: providing a mold having a plurality of truss wallhoneycomb-shaped cavities; depositing one or more materials into saidmold cavities to form the truss wall members; and removing the mold. 23.The method of fabricating a vented truss wall honeycomb structure ofclaim 22 further comprising joining one or more perimeter-orientedfacing skins to the honeycomb structure.
 24. The method of fabricating avented truss wall honeycomb structure of claim 23 wherein joining thefacing skins to the honeycomb structure comprises at least one ofsoldering, brazing, welding, diffusion bonding, chemical welding,adhesives, and pressing.
 25. The method of fabricating a vented trusswall honeycomb structure of claim 22 further comprising functionallygrading at least one of the honeycomb cells, the truss wall openings,the truss wall members, and the truss walls.
 26. A method of fabricatinga truss wall honeycomb structure having a plurality of honeycomb cellsarranged in a hierarchical order and having a plurality of truss walls,each truss wall including a plurality of members and a plurality oftruss wall openings, the method comprising: additively depositingmaterial to construct the honeycomb structure; and joining one or moreperimeter-oriented facing skins to the honeycomb structure.
 27. Themethod of fabricating a vented truss wall honeycomb structure of claim26 wherein joining the facing skins to the honeycomb structure comprisesat least one of soldering, brazing, welding, diffusion bonding, chemicalwelding, adhesives, and pressing.
 28. The method of fabricating a ventedtruss wall honeycomb structure of claim 26 further comprisingfunctionally grading at least one of the honeycomb cells, the truss wallopenings, the truss wall members, and the truss walls.
 29. A method offabricating a truss wall honeycomb structure having a plurality ofhoneycomb cells arranged in a hierarchical order and having a pluralityof truss walls, each truss wall including a plurality of members and aplurality of truss wall openings, the method comprising: extruding andselectively removing material to construct the honeycomb structure; andjoining one or more perimeter-oriented facing skins to the honeycombstructure.
 30. The method of fabricating a vented truss wall honeycombstructure of claim 29 wherein joining the facing skins to the honeycombstructure comprises at least one of soldering, brazing, welding,diffusion bonding, chemical welding, adhesives, and pressing.
 31. Themethod of fabricating a vented truss wall honeycomb structure of claim29 further comprising functionally grading at least one of the honeycombcells, the truss wall openings, the truss wall members, and the trusswalls.
 32. A method of fabricating a truss wall honeycomb structurehaving a plurality of honeycomb cells arranged in a hierarchical orderand having a plurality of truss walls, each truss wall including aplurality of members and a plurality of truss wall openings, the methodcomprising: aligning and joining the plurality of honeycomb cells toform a multi-cell truss wall honeycomb structure; and joining one ormore perimeter-oriented facing skins to the honeycomb structure.
 33. Themethod of fabricating a vented truss wall honeycomb structure of claim32 wherein joining the facing skins to the honeycomb structure comprisesat least one of soldering, brazing, welding, diffusion bonding, chemicalwelding, adhesives, and pressing.
 34. The method of fabricating a ventedtruss wall honeycomb structure of claim 32 further comprisingfunctionally grading at least one of the honeycomb cells, the truss wallopenings, the truss wall members, and the truss walls.